Genetic Material Expression (PDF)

Components of DNA • DNA is a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group • The nitrogenous bases can be adenine (A), thymine (T), guanine (G), or cytosine (C) • The composition and arrangement of nucleotides varies from one individual to the next • A...

Components of DNA • DNA is a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group • The nitrogenous bases can be adenine (A), thymine (T), guanine (G), or cytosine (C) • The composition and arrangement of nucleotides varies from one individual to the next • Almost like an individual code Figure 16.5 Structure of DNA • It was discovered that the number of adenine (A) and Thymine (T) bases are always equal to each other, and the number of Guanine (G) and Cytosine (C) bases are always equal to each other. Figure 16.5 Figure 16.6 Structural Model of DNA • Maurice Wilkins and Rosalind Franklin used a technique called X-ray crystallography to study molecular structure • Franklin produced a picture of the DNA molecule using this technique • Franklin’s images enabled James Watson and Francis Crick to deduce that DNA was helical • The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix History of Controversy https://sciencehistory.org/education/scientific-biographies/james-watson-francis-crick-maurice-wilkins-and-rosalind-franklin/ Double Helix • DNA molecules are made up of two strands, forming a double helix • Two outer sugar-phosphate backbones rotate around paired nitrogenous bases in the molecule’s interior. • Backbones are antiparallel (subunits run in opposite directions). Figure 16.07ba Nucleotide Pairing • Adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C) • Therefore, in any organism the amount of A = T, and the amount of G = C Figure 16.9 What if thymine and cytosine traded places? labxchange.org 5′ end 3′ end DNA nucleotide Sugar-phosphate backbone 3′ end Figure 16.07ab 5′ end @microbiologistlablife 1. Recall the organization of genetic material in the cell and how it is organized and distributed during mitosis. Learning Objectives 2. Be familiar with DNAs structural components and their function. 3. Understand the processes required for genes present on DNA (enclosed in the nuclear envelope) to become expressed (in the cytoplasm in the cell). What is a gene? • Genes are segments of our genome that encodes the information for making proteins • Think of proteins as the brick and mortar that make up our cells and tissues. • Essentially are segments of DNA made up of nucleotides along with their specific nitrogenous bases: A, G, C, and T • Together those 4 bases encode for all information that is used to make a functioning biological organism! Figure 17.05 Central Dogma • Genetic information flows in one direction • From DNA in the nucleus, to RNA, to protein (or in some organisms from RNA directly to protein) • How do you go from DNA to a Protein? Figure 17.UN01 Start in the Nucleus - Transcription Nuclear envelope TRANSCRIPTION RNA PROCESSING NUCLEUS DNA Pre-mRNA mRNA CYTOPLASM (b) Eukaryotic cell Figure 17.04b_1 Prokaryotes vs Eukaryotes Nuclear envelope TRANSCRIPTION TRANSCRIPTION DNA RNA PROCESSING NUCLEUS CYTOPLASM DNA Pre-mRNA mRNA mRNA CYTOPLASM (a) Bacterial cell (b) Eukaryotic cell Figure 17.04b_1 The Genetic Code • How are the instructions for assembling amino acids into proteins encoded into DNA? • There are 20 amino acids, but there are only four nucleotide bases in DNA (A, G, C, T) • How is this possible?! Figure 5.14 Figure 17.5 Codons • The flow of information from gene to protein is based on a triplet code • Genes are transcribed into complementary nonoverlapping three-nucleotide “words” carried by mRNA • These words are then translated into a chain of amino acids, forming a polypeptide Figure 17.5 Going from gene to protein • The non-template strand is called the coding strand because the nucleotides of this strand are identical to the codons, except that T is replaced by Uracil (U) in RNA • Each codon specifies the amino acid (one of 20) to be placed at the corresponding position along a polypeptide Figure 17.04b_3 Figure 17.5 Nuclear envelope TRANSCRIPTION RNA PROCESSING NUCLEUS DNA Pre-mRNA mRNA CYTOPLASM TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell Figure 17.6 Figure 17.5